There is a conventionally-known method according to which a mobile device outputs a signal, and an on-board device that has received the signal performs specific control on a vehicle door. JP 2001-234653A discloses a method according to which a mobile device periodically transmits an unlock request signal, and an on-board device that has received the unlock request signal unlocks a vehicle door after performing authentication on the mobile device based on the signal.
Also, JP 2009-24454A discloses a method according to which a mobile device (an instruction apparatus) transmits a reservation signal based on an operation input by a user, and an on-board device (a vehicle-side control apparatus) that has received the reservation signal detects whether or not the user is present near a vehicle door, and opens the vehicle door upon detecting the presence of the user.
However, with the method disclosed in JP 2001-234653A, the mobile device keeps regularly transmitting the unlock request signal while the mobile device is turned ON. Therefore, the on-board device unlocks the vehicle door even if the user does not intend to unlock the vehicle door, which is undesirable in terms of security. Also, with the method disclosed in JP 2009-24454A, the user cannot check whether or not the on-board device has properly received the reservation signal. Therefore, with the method disclosed in JP 2009-24454A, there is a problem in which, although the user has moved closer to a vehicle door after causing the mobile device to transmit a reservation signal, the user cannot open the vehicle door because the on-board device could not receive the reservation signal, thus degrading the convenience.
An object of the present application is to provide a vehicle communication system and a mobile device that make it possible to automatically open a vehicle door without impairing security or convenience.